Rubber is widely used in aerospace, weaponry and equipment, automobiles, ship, delicate machinery, petrochemical industry, electricity and many other fields. It is easily damaged by light, heat, rain, snow, oxidization, physical stresses and chemical corrosion and other environmental and external forces. Rubber is prone to aging, which means its chemical structure is damaged, its appearance becomes rough, and the mechanical properties are deteriorated. Aging is an important factor affecting the service life of rubber. Many rubber products, such as inner tube of tire and rubber products used as sealing materials, should have low air permeability in addition to good mechanical properties. In this paper, the gas permeability of rubber before and after aging was tested, and the effect of aging on the gas barrier performance of rubber is compared.

In this test, we used a brand of tire rubber as the test sample and referred to ISO 2782 “Rubber, vulcanized or thermoplastic-Determination of permeability to gases” to test the nitrogen permeability before and after the rubber aging.

The instrument used in this test is Labthink VAC-V2 Gas Permeability Tester. The testing instrument based on the principle of differential pressure method obtains the gas transmission of materials by measuring the gas pressure change caused by gas permeation, therefore, it can test the gas transmission of various gases. During the test, the sample is clamped to the test chamber, dividing the test chamber into two chambers, the upper chamber is filled with test gas, the lower chamber is a vacuum environment, the upper chamber gas permeates into the lower chamber through the sample, causing the gas pressure in the lower chamber to change, and the gas permeability of the material can be obtained by monitoring the change of the pressure in the lower chamber with the permeation time. The high gas permeability of the sample indicates a poor barrier performance of the material; on the other hand, if the gas permeability is low, the material’s barrier performance is high.

Test procedure

(1) Cut three specimens in 97 mm diameter from the non-aged samples, and clamp the samples in the sequence of “applying grease – putting filter paper – mounting samples – tightening the test chamber cover”.

(2) Connect the instrument with nitrogen gas supply. Set the sample name, test temperature, humidity, test mode and other parameter on the control software, click the test option, turn on the vacuum pump and start the test. The instrument runs the test according to the set parameters, and the test results are displayed after the test is accomplished.

(3) Test the nitrogen transmission of the aged sample following to the above operation.

Test results

Take the arithmetic mean value of the test results of three specimens of each sample as the nitrogen transmission of the sample. Before aging, the nitrogen transmission of the sample is 24.893 cm³/(m²·24h·0.1MPa), and after aging, the nitrogen transmission of the sample 20.746 cm³/(m²·24h·0.1MPa).

Conclusion

The nitrogen transmission of the aged sample is lower than that of the aged sample. This shows that the barrier performance of the aged rubber sample to nitrogen is not decreased, but increased. This phenomenon may be related to the crosslinking reaction of the molecular chain in the aging process of the sample. In terms of the test process, the control of the test parameters is stable, which ensures the accuracy of the test results. Three samples are tested in one test, which improves the test efficiency.